Anthropogenic and environmental factors affect the tree line position of Fagus sylvatica along the Apennines (Italy)

Abstract

Aim High‐elevation forest line or tree line is an ecological ecotone representing the upper elevation thermal limit for forest development. The current tree line position is the result of the past human activity interacting with climatic and topographic conditions. In this study, we investigate how climate, local topographic factors and anthropogenic disturbance currently affect tree line distribution. Location Apennine Mountains, 900 km latitudinal gradient along the Italian Peninsula. Methods Overall, 302 mountain peaks were studied, comprising 3,622 km of measured tree lines. The position of the Fagus sylvatica tree line in all peaks was assessed and correlated with 58 selected variables representing climate, topography and human disturbance. Results The mean tree line elevation was 1,589 m a.s.l., with considerable variability among peaks. Contrary to our expectations, the tree line elevation was lower in the warmer southerly exposed slopes compared to north‐facing aspects, where we found the highest tree line (2,141 m a.s.l.). Correlation analysis indicates that both climatic and human density variables are associated with tree line elevation, with the climate having more influence in high elevation mountains, while human impact plays a prominent role in low elevation mountain peaks. Specifically, we found negative correlations between density of the resident population around each peak and tree line elevation at all examined dates (1861, 1921, and 2011), suggesting a pervasive negative impact of human activity on tree lines. As regards climatic variables, tree line elevation showed a stronger negative correlation with winter and spring months temperature than with mean annual temperature. Noteworthy, climatic variables had stronger effect on high elevation peaks (>1,900 m a.s.l.) compared with low elevation ones (<1,900 m a.s.l.). Main Conclusion Our data provide evidence that the current position of the F. sylvatica tree line in the Apennines is heavily depressed as a result of a complex interaction between climatic factors and the past human pressure.

Climatic and anthropogenic factors explain the variability of Fagus sylvatica treeline elevation in fifteen mountain groups across the Apennines

“…To determine the current F. sylvatica treeline elevation we used a recently published data set (Bonanomi et al 2018). Briefly, the Apennines treeline position was mapped on Google Earth Pro™ (Google Inc., Mountain View, CA, USA), using the time series images ranging from 2004 to 2011, with which the treeline boundaries of all Apennine mountain peaks were digitized, amounting to a total of 302 mountains.…”

“…up to the treeline, mixed with Abies alba only in more thermophilous low-elevation Mediterranean beech forests (Di Pasquale et al 2014;Rita et al 2014). Recently, in a study on F. sylvatica treeline elevation in the Apennines, Bonanomi et al (2018) reported an average elevation of 1589 m a.s.l., with considerable variability among peaks ranging from less than 1000 m a.s.l. to the highest site reaching 2141 m a.s.l.…”

“…Limiting temperature, however, at local scale interacts with mountain topography, soil quality, and biotic factors like herbivores and anthropogenic disturbance that may substantially change treeline shape and elevation (Macias-Fauria and Johnson 2013;Ameztegui et al 2016). In this regard, several studies have shown that drought, recurrent fire and logging can dramatically depress treeline elevation compared to the species potential based on climatic stress alone (Piper et al 2016;Bonanomi et al 2018). For instance, aspect controls the amount of solar radiation reaching surfaces (Monteith and Unsworth 2013), thus affecting air, soil and vegetation temperatures (Wieser and Tausz 2007).…”

“…Thus treeline elevation is expected to be higher on south-facing warmer slopes than on their cooler northfacing counterparts. However, in the Mediterranean area, which is frequently subjected to drought and soil moisture depletion in the summer season, south-facing slopes can be more prone to drought than north-facing slopes, causing a substantial lowering of treeline elevation (Piper et al 2016;Bonanomi et al 2018).…”

Treeline Research—From the Roots of the Past to Present Time. A Review

“…In addition, historical displacement of treeline by humans and a delay of treeline response to climate change also play a major role in the respect. Hence, at finer scales, treeline position is often out-of-phase with climate (e.g., [1,[161][162][163][164][165][166][167][168][169][170][171][172][173][174][175][176]). Global overviews, necessarily disregarding the local differences, may easily overemphasize coarse drivers such as temperature [167,177,178].…”